Mucosal surfaces must allow the exchange of metabolites required for life into the host and excretion/exclusion of wastes and toxins out of the host, while also maintaining a first line of defense against invasive microbes. However, mucosal inflammation, elicited to combat microbial infection, can also damage the integrity of the mucosal barrier, if not controlled. Many mucosal surfaces are in constant or transient contact with microbes, yet the molecular mechanisms governing the extent of the inflammatory response at the mucosal surface and the molecular basis of a protective adaptive mucosal response are poorly understood. This proposal will investigate these mechanisms by assembling an experienced team of investigators with diverse and complimentary expertise to investigate the mucosal immune defense mechanisms of the urinary bladder against bacterial infection. We will test the hypothesis that the integration of immune signaling pathways within the first few hours of bacterial infection, including those from the bladder epithelium, constitute a mucosal immune checkpoint that has a profound impact upon the outcome of disease and bladder mucosal remodeling. The proposed research will utilize a simple and highly tractable murine model of lower urinary tract bacterial infection to probe these immune defense pathways of the bladder mucosa during acute, chronic and recurrent infection. The experimental approaches proposed will provide critical insights in the field of mucosal immunology. These studies will investigate the role of specific innate signaling pathways (Aim 1) and cellular responses (Aim 2) early in acute infection of naive mice, and the role of adaptive changes such as chronic inflammatory cell infiltrates and IgA production in establishing sensitivity to or protection from recurrent infection (Aim 3). These investigations will reveal new details of the mechanisms of mucosal defense against bacteria, broadening the understanding of the regulation of mucosal inflammation and the signaling between mucosal epithelia and immune cells, and thus advance our understanding of chronic and recurrent infection susceptibility and protection. These insights will contribute to the development of novel vaccines and therapeutics targeting the mucosa.